The present invention relates to a light-sensitive silver halide emulsion, particularly to a tabular silver halide grain emulsion for photography.
In general, silver halide emulsions containing tabular silver halide grains (referred to as xe2x80x9ctabular grainsxe2x80x9d hereinafter), especially thin tabular grains, have the following advantages in their photographic characteristics:
(1) since the surface area/volume ratios (referred to as xe2x80x9cspecific surface areasxe2x80x9d hereinafter) of tabular grains are great and large quantities of sensitizing dyes can be adsorbed to the tabular grain surfaces, the emulsions have high spectral sensitization sensitivities as compared with their intrinsic sensitivities,
(2) when emulsions containing tabular grains are coated on a support and dried, the grains are aligned in parallel with the support surface, so the coating layers can be made thin and the resulting photographic light-sensitive material is improved in sharpness,
(3) since little scattering of light is caused by tabular grains, images of high resolution is obtained, and
(4) since the tabular grains have low sensitivity to blue light, using them in a green-sensitive or a red-sensitive layer enables removal of an yellow filter from the emulsion layer. Therefore, such emulsions have so far been used in commercially available high-speed light-sensitive materials.
In Japanese Patent Publication Nos. 44132/1994 and 16015/1993 are disclosed the tabular emulsion grains having aspect ratios of at least 8. The term xe2x80x9caspect ratioxe2x80x9d as used herein is defined as a diameter/thickness ratio of each individual grain. The diameter of each individual grain refers to the diameter of a circle having the same area as the grain""s projected area determined by observation under a microscope or an electron microscope. The thickness of each individual grain refers to the distance between two parallel surfaces forming the tabular grain.
Further, Japanese Patent Publication No. 36374/1992 discloses the color photographic light-sensitive material which contains tabular grains having a thickness of less than 0.3 xcexcm and a diameter of at least 0.6 xcexcm in at least either of the green-sensitive and red-sensitive emulsion layers and thereby achieves improvements in sharpness, sensitivity and graininess. In recent years, on the other hand, silver halide light-sensitive materials have advanced in sensitivity increase and format reduction, and color photosensitive materials having higher sensitivities and improved image qualities have been desired strongly. Therefore, silver halide grain emulsions having higher sensitivity and more excellent graininess have been required. However, conventionally known tabular silver halide emulsions are insufficient to meet these requirements, and so stepped-up improvements in photographic characteristics are expected.
Additionally, tabular grains having greater aspect ratios can have the greater specific surface areas, and so they can make good use of the above-described advantages of tabular grains.
However, tabular grains enable adsorption of sensitizing dyes in greater amounts but, at the same time, have a defect of reflecting a greater proportion of light incident thereon. Therefore, it is difficult to obtain an increase in light absorption as expected.
On the other hand, silver iodide exhibits a face centered cubic crystal lattice structure under very high level of pressure (3,000 to 4000 times the atmospheric pressure) alone. The silver halide of this structure is referred to as "sgr"-phase AgI, and irrelevant to silver halide photography. Normally, the most stable crystal structure of silver iodide is a hexagonal wurtzite type, and the silver iodide of this crystal structure is generally referred to as xcex2-phase AgI. The photographically useful, sufficiently stable, secondary crystal lattice structure of silver iodide is a face centered cubic zinc-blending type crystal structure, and the silver iodide of this structure is generally referred to as xcex3-phase AgI. Silver halide emulsions containing xcex2-phase AgI, xcex3-phase AgI and AgI having a mixture of these phases, respectively, have been made. The fourth crystallographic form of silver iodide is xcex1-phase, namely a body centered cubic structure. According to the description in T. H. James, The Theory of Photographic Process, page 1, the formation of this crystal structure requires the temperature of 146xc2x0 C. And the bright yellow silver iodide reported in U.S. Pat. No. 4,672,026 to Daubendiek is believed to be xcex1-phase AgI. (The descriptions at pages 1 to 5 of the book compiled by James relate to these crystal lattice structures and these studies.)
High-iodide silver halide grains have a marked advantage over silver halide grains of face centered cubic crystal lattice structure in that they have higher intrinsic absorption in the short blue portion (400 to 450 nm) of spectrum. In particular, high-iodide silver halide is generally identified as silver halide that exhibits an absorption peak at 425 nm missing in the absorption spectra of silver chloride and silver bromide, has a crystal lattice structure different from the face-centered cubic crystal structure and contains at least 97 mole % of iodide (high-iodide), based on total silver, namely only a minute amount of bromide and/or iodide. U.S. Pat. No. 4,184,878 to Maternaghan is an example of the high-iodide silver halide emulsion.
However, high-iodide silver halide grains are difficult to sensitize and develop with commercial developers, and these difficulties greatly inhibit their use for latent image formation.
Under these circumstances, it has been proposed from time to time to join a high-iodide phase to the surface of tabular silver halide grains having a face-centered hexagonal crystal lattice structure with the aim of exploiting both the advantages of tabular grains and high absorptivity of silver iodide, and further with the intention of supplementing defects of tabular grains and silver iodide.
U.S. Pat. No. 4,471,050 discloses selective attachment of nonisomorphic silver salts to edges of silver halide host grains without recourse to any additional site director. In these non-isomorphic silver salts are included silver thiocyanate, xcex2-phase AgI (exhibiting a hexagonal wurtzite type crystal structure), xcex3-phase AgI (exhibiting a zinc-blending type crystal structure), silver phosphates (including meta- and pyrophosphates) and silver carbonate. None of these non-isomorphic silver salts exhibit the face-centered cubic crystal structure of the type which is observed in photographic silver halides (namely the isomorphic face-centered cubic crystal structure of rock salt type). In fact, the sensitivity increase produced by nonisomorphic silver salt epitaxy was smaller than that attained by comparative isomorphic silver salt epitaxial sensitization.
Japanese Patent Application (Laid-Open) No. 2000-2959 discloses silver halide tabular grains having, on the main surfaces of {111} tablet having a thickness of 0.1 xcexcm or below, ruffled surfaces formed of minute protrusions containing 10 mole % or less of iodide and having projected area diameters of 0.15 xcexcm or below. The present invention can provide tabular silver halide grains enabling adsorption of sensitizing dyes in an increased amount and reduced reflection of light since the grains are increased in specific surface area without decrease in thickness. However, the objective for incorporating silver iodide in those protrusions was not to improve absorption of light, but to maintain structural stability of the protrusions. Therefore, it is hard to say that those tabular grains made good use of photographically useful properties of silver iodide, including highly efficient absorption of light.
U.S. Pat. No. 5,604,086 is one illustrative instance of emulsions containing tabular grains of rock salt-type face-centered cubic lattice structure which have epitaxially grown high-iodide silver halide crystals on the main surfaces thereof. Therein, it is disclosed that the tabular grains are composite grains having epitaxial phases of high iodide contents on the main surfaces of {111} tabular grains or {100} tabular grains, and the high-iodide epitaxial phases form discrete plates having triangular and hexagonal boundaries and can yield a great improvement in absorptivity of blue light. However, those tabular grains have problems that the epitaxial phases deposited are distributed unevenly among the grains, and besides, the high-iodide phases are present on the lateral faces (i.e., the side surface) also to retard the rate of development.
Therefore, an object of the present invention is to achieve a sensitivity increase by utilizing strong absorption of the blue light having a short wavelength by high-iodide phase, and besides, to provide a silver halide emulsion ensuring fast ratye of development.
Ideally, a silver halide emulsion having a high sensitivity/fog ratio can be provided by depositing high-iodide epitaxy on the main surfaces and lowering an iodide content in the lateral faces (i.e., the side surface).
More specifically, the object described above is attained with the following embodiments 1 to 16 of the present invention:
1. A silver halide emulsion comprising silver halide grains, at least 50% of total projected area of the silver halide grains being accounted for by silver halide tabular grains having {111} main surfaces (also referred to as xe2x80x9chost tabular grainsxe2x80x9d hereinafter), wherein the main surface of the tabular grains are subjected to junction with epitaxial phases formed of silver halides comprising at least 97 mole % of silver iodide (high-iodide epitaxial phases) and the lateral face of the host tabular grain comprises silver halide having silver iodide contents of substantially 5 mole % or below.
2. A method of preparing a silver halide emulsion as described in Embodiment 1, comprising sequentially joining high-iodide epitaxial phases to host tabular grains and depositing silver halide phases having a low silver iodide content intentionally on lateral faces of the host tabular grains.
3. The silver halide emulsion as described in Embodiment 1, wherein the inner part occupying less than 80% of the total silver from the center in the host tabular grain part has an average silver iodide content of at least 5 mole % and an outer part which surrounds the inner part has an average silver iodide content of 5 mole % or less, and a difference in silver iodide content between the inner part and the outer part is in the range of 0 to 10 mole %.
4. The silver halide emulsion as described in Embodiment 1, wherein the host tabular grains comprise high silver iodide-content surface layers and low silver iodide-content surface layers formed on the fringes of the high silver iodide-content surface layers, and further the high silver iodide-content surface layers and the low silver iodide content surface layers are exposed at the main surfaces in an areal ratio from 2:1 to 9:1 (in other words, a ratio of the area of the high silver iodide-content surface layers exposed at the main surfaces to the area of the low silver iodide-content surface layers exposed at the main surfaces is from 2:1 to 9:1).
5. The silver halide emulsion as described in any one of Embodiments 1, 3 and 4, wherein the host tabular grains each contain dislocations formed during the grain growth in an outer region of each individual main surface which is situated far from the main surface""s center by 80% or more of a distance between the center and the periphery of the main surface, and further the host tabular grains containing dislocations make up at least 90% of the total grains.
6. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 5, wherein the silver iodide contents in the lateral faces are substantially 1 mole % or below.
7. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 6, wherein the host tabular grains have projected area diameters of at least 2 xcexcm.
8. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 7, wherein at least 90% of total projected area of the host tabular grains are accounted for by tabular grains having aspect ratios of at least 2.
9. The silver halide emulsion as described in any one of Embodiments 1, and 3 to 8, wherein at least 60% of the epitaxial phases are formed of silver halides containing at least 97 mole % of silver iodide.
10. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 9, wherein the high-iodide epitaxial phases account for at least 10 mole % of total amount of silver.
11. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 10, wherein an occupying areal proportion of the high-iodide epitaxial phases subjected to junction onto the main surfaces of each host tabular grain is within xc2x110% of an average occupying areal proportion for all the grains.
12. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 11, wherein the silver halide grains are subjected to reduction sensitization.
13. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 12, wherein the silver halide grains contain a photographically useful dopant.
14. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 13 and a method of preparing the emulsion, wherein grain growth of at least 10% of the host tabular grains, based on silver, is performed in a vessel by adding thereto fine grains of silver iodobromide formed in a vessel other than the vessel for the grain growth.
15. The silver halide emulsion as described in any one of Embodiments 1 and 3 to 14, wherein the silver halide grains have a corner portion subjected to junction with epitaxial phases of silver halide having iodide contents of substantially 10 mole % or below.
16. The method of preparing a silver halide emulsion as described in Embodiment 2, wherein the high-iodide epitaxial phases are formed under the following conditions (1) and/or (2) and then silver halide phases with low silver iodide contents are disposed on the lateral faces of the tabular grains:
(1) pAg is maintained to less than 6.4
(2) a compound having (100) face selectivity is present.
The present invention is illustrated below in further detail.
With respect to the present tabular-grain part (referred to as xe2x80x9chost tabular grainxe2x80x9d), the main surfaces thereof are {111} faces. Tabular silver halide grains which each have one twin plane or two or more parallel twin planes are generically called xe2x80x9ctabular grains having {111} faces as main surfacesxe2x80x9d. The term twin plane means the {111} face with respect to which all pairs of lattice ions on opposite sides are mirror images of each other. When viewed from above, these tabular grains have the shape of a triangle or a hexagon, or the shape rounded off in the corners of a triangle or hexagon. The triangular, hexagonal or rounded-off tabular grains each have mutually parallel outer surfaces in the shape of a triangle or hexagon, or in the shape rounded off in the corners of a triangle or hexagon.
The epitaxial phases according to the present invention are present on the main surfaces of host tabular grains, and besides, these phases have high iodide contents of at least 97 mole % (sometimes they are abbreviated as xe2x80x9chigh-iodide epitaxial phasesxe2x80x9d). Silver iodide has high shape stability because of low solubility, and can achieve a gain in absorption of blue light. When silver halides other than silver iodide are contained in large amounts, optical absorptivity is lowered. The mixing of other halides into the high-iodide epitaxial phases is a consequence of depositing high-iodide epitaxial phases by introduction of silver and iodide ions into a host tabular grain emulsion in the presence of bromide and/or chloride ions in a state of equilibrium with the host tabular grains. Minimizing the mixing of halides other than iodide into high-iodide epitaxial phases is effective in gaining highly effective optical absorption. It is favorable for this purpose that at least 60% of the epitaxial phases formed are made up of silver halides having an iodide content of at least 97 mole %.
When the present emulsion (i.e., the emulsion of the present invention) is exposed to light of short wavelengths from 400 to 450 nm, the photons are absorbed by not only tabular grains but also a number of high-iodide epitaxial parts present on the grains"" main surfaces. The epitaxial phases are present on the topside and the underside of each tabular grain, and so from 60 to 70% of the total photons of short blue light can be absorbed at the high-iodide epitaxial parts present on both topside and underside. In the case where the tabular grains have high-iodide epitaxial parts only on their fringe areas and vertexes, photons capable of being absorbed thereby becomes very scarce. Therefor, it is undesirable to form the high-iodide epitaxial phases only on the fringe areas of main surfaces.
In addition, in the case where the high-iodide epitaxial phases are subjected to junction to the fringe areas and lateral faces (i.e., side surfaces) of tabular grains, development is markedly inhibited, and optical absorption by the high-iodide epitaxial phases cannot be reflected in sensitivity. In order to improve these conditions in the present invention, many high-iodide epitaxial phases are formed on the main surfaces of host tabular grains and iodide contents in the lateral faces of tabular grains are controlled to 5 mole % or below, preferably 2 mole % or below. Thus, the problems about development and optical absorption have been resolved.
More specifically, the development trouble is improved in the present invention through success in controlling lateral iodide contents to 5 mole % or below by disposing low-iodide silver halide phases on the lateral faces of host tabular grains after junction of high-iodide epitaxial phases. For the control of lateral iodide content, it is important to deposit high-iodide epitaxial phases on the central areas of host tabular grains"" main surfaces, but not to deposit high-iodide epitaxial phases on the fringe areas of host tabular grains"" main surfaces and the host tabular grains"" lateral faces, and further to prevent mixed crystallization by dissolution/recrystallization of high-iodide epitaxial phases. Conditions meeting these requirements are described in detail in Examples.
It is appropriate that the present host tabular grains (i.e., the host tabular grains of the present invention) each have a silver iodide content of at least 5 mole %, preferably at least 7 mole %, based on the amount of silver, in a three-dimensional region occupying the central part and containing 80% of the total silver forming each individual grain. In the outside of this region, the suitable silver iodide content is 5 mole % or below, preferably 2 mole % or below, on a silver bases. The suitable difference in silver iodide content between these two regions is from 0 to 10 mole %. Herein, the center of each grain means the position at which there is the center of gravity of each grain. By having such a silver iodide distribution, the host tabular grains in themselves can gain absorption of blue light in addition to high-iodide epitaxial phases, resulting in achievement of high optical absorption.
In the present invention, it is desirable to use host tabular grains made up of high-iodide surface and low-iodide surface layers formed on fringes of the high-iodide surface layers. The suitable silver iodide contents in the high-iodide surface layers of the host tabular grains is at least 5 mole %, preferably at least 10 mole %, while those in the low-iodide surface layers are not more than 3 mole %, preferably not more than 1 mole %. And it is appropriate that the areal ratio between those two surface layers exposed at each main surface (the ratio of the area of the high-iodide surface layer exposed at each main surface to the area of the low-iodide surface layer exposed at each main surface) be from 2:1 to 9:1. The high-iodide epitaxial phases are deposited preferentially on the high-iodide surface layers. As a result, it becomes possible to control the iodide contents in the fringe areas and lateral faces to 5 mole % or below. After deposition of high-iodide epitaxial phases on the host grains, silver halide phases having low silver iodide contents are further disposed on the lateral faces of the host tabular grains, and enable an increase in development speed.
In the present invention, the lateral silver iodide content is determined by the following method.
The tabular silver halide grains in a silver halide photographic emulsion are extracted through gelatin degradation with a proteolytic enzyme, and then enveloped in methacrylic resin, and further cut into slices about 500 xc3x85 in thickness by means of a diamond cutter. From these slices are picked out slices having visible fault planes perpendicular to parallel main surface pairs of tabular silver halide grains. As to each of the tabular silver halide grains whose fault planes are visible, the silver halide layer portion extending from the lateral surface to an inward distance of 100 xc3x85 is examined by spot analysis performed in accordance with analytical electron microscopy wherein the spot diameter is narrowed down to 50 xc3x85, preferably 20 xc3x85, thereby determining the lateral silver iodide content.
Further, it has been discovered that the present host tabular grains can produce greater effects by containing dislocation lines generated during the growth thereof. And it is appropriate for the host tabular grains to contain the dislocation lines in an outer region of each individual main surface which is situated far from the main surface""s center by 80% of a distance between the center and the periphery of the main surface. Description of techniques to introduce dislocation lines into silver halide grains under control can be found in Japanese Patent Application (Laid-Open) No. 230238/1988. According to this document, dislocations can be introduced by forming specified phases having high silver iodide contents in the interior of tabular silver halide grains having an average grain diameter/grain thickness ratio of at least 2, and then covering these phases on the exterior with phases having iodide contents lower than the phases having high silver iodide contents. The introduction of dislocations can produce various effects, including a rise insensitivity, an improvement in keeping quality, an increase in latent-image stability and a reduction of pressure mark. In the present invention disclosed in the document cited above, the dislocations are introduced predominantly on the edges of tabular grains. On the other hand, U.S. Pat. No. 5,238,796 describes the tabular grains in the center part of which dislocations are introduced. In this document, it is disclosed that dislocations are introduced by epitaxially depositing silver chloride or chlorobromide on normal crystal grains and subjecting the epitaxial deposits to physical ripening and/or halogen conversion. By the introduction of these dislocations, effects of increasing the sensitivity and reducing the pressure mark can be achieved. The dislocation lines contained in silver halide grains can be observed by the direct method using a transmission electron microscope at a low temperature as described in J. F. Hamilton, Photo. Sci. Eng., 1967, 11, 57 and T. Shiozawa, J. Soc. Photo Sci., JAPAN, 1972, 35, 213. More specifically, silver halide grains extracted from an emulsion while exercising care to avoid applying a pressure on the level of causing dislocations to the grains are put on a mesh for observation with an electron microscope, and the observation of these grains by transmission method is carried out under cooling so as to prevent damage (printout) caused by electron beams. Therein, as the grains are more resistant to transmission of electron beams the greater they are in thickness, the use of an electron microscope of higher pressure type (200 keV or higher with respect to the thickness of 0.25 xcexcm) enables the clearer observation. From the photographs of grains taken in the above-described manner can be determined the positions and the number of dislocation lines present in each individual grain viewed from the plane perpendicular to the main surface.
The suitable diameter (equivalent circle diameter) of the present host tabular grains is from 2 xcexcm to 20.0 xcexcm, preferably from 3.0 xcexcm to 10 xcexcm. Silver halide grains having projected-area diameters of at least 2.0 xcexcm account for at least 50% of the total projected area. The suitable equivalent sphere diameter is from 1.0 xcexcm to 5.0 xcexcm, preferably from 1.2 xcexcm to 3 xcexcm. The term xe2x80x9cequivalent sphere diameterxe2x80x9d as used herein means the diameter of a sphere equivalent in volume to each individual grain. In addition, the suitable aspect ratio is from 2 to 50, preferably from 10 to 30. The term xe2x80x9caspect ratioxe2x80x9d as used herein is defined as a value obtained by dividing the projected-area diameter of a grain by the grain""s thickness.
As the present host tabular grains, it is advantageous to use tabular grains which are monodisperse with respect to the distribution of their equivalent circle diameters. In regard to the monodisperse distribution, Japanese Patent Application (Laid-Open) No. 11928/1988 and Japanese Patent Publication No. 61205/1993 disclose the monodisperse hexagonal tabular grains, and Japanese Patent Application (Laid-Open) No. 131541/1989 discloses the monodisperse circular tabular grains. Further, Japanese Patent Application (Laid-Open) No. 838/1990 discloses the emulsion wherein at least 95%, on a projected-area basis, of the total silver halide grains are tabular grains which each have two twin planes parallel to the principal surfaces and the size distribution of these tabular grains is monodisperse. And EP-A-514742 discloses the tabular grain emulsion which is prepared using a polyalkylene oxide block copolymer and has a variation coefficient of 10% or below with respect to the grain size distribution.
As a method of preparing host tabular grains used in the present invention, or tabular grains of the type which have {111} main surfaces, the methods disclosed in U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306 and 4,459,353, and Japanese Patent Application (Laid-Open) Nos. 179226/1997 and 92057/2001 can be adopted. In these references, the techniques for using those grains are also disclosed. Further, as disclosed in Japanese Patent Application (Laid-Open) No. 214331/1994, tabular grains can be formed by once forming seed crystals by nucleation, and then preparing the seed crystals grow by adding silver salt and halide solutions under conditions that pH and pAg values are adjusted so as to fit the grain growth.
Dyes ideal for use in the present invention are blue-sensitive dyes (dyes sensitive to light of wavelengths ranging from 400 to 500 nm) which each show a maximal absorption peak having a half width of about 100 nm in the region of 400 to 500 nm when they are applied to general tabular grains. However, dyes providing the half-peak width of 100 nm are little known. In other words, there are no dyes whose absorption peaks have half widths equivalent to the wavelength spread of the blue spectrum. In the case of general blue-sensitive dyes, the half-peak width thereof is 50 nm or below. When one or more of dyes having maximal absorption at the longer wavelengths is combined with the present emulsion, blue absorption with higher efficiency can be obtained over the entire blue region of spectrum because the absorption peak of high-iodide epitaxial phases is 427 nm.
When sensitizing dyes are not present, short blue photons are absorbed in high-iodide epitaxial parts and photohole-photoelectron pairs are formed. The photoelectrons migrate freely into host tabular grains via junctions between the host tablet and the high-iodide epitaxial phases, while the photoholes are trapped in the high-iodide epitaxial parts. Therefore, photoholes and photoelectrons are separated and re-coupling between them is inhibited. Thus, the high-iodide epitaxial phases can contribute to supply of many photoelectrons for latent-image formation; as a result, they can function so as to enhance the sensitivity of emulsion grains as a whole.
Elevation of short blue light absorptivity can be achieved by increasing the thickness of the high-iodide epitaxial phases and the area taken up by these phases. For a further rise in light absorptivity, it is desirable to increase the proportion of the high-iodide epitaxial phases present on the main surfaces of host tabular grains. More specifically, it is appropriate that the high-iodide epitaxial phases account for at least 25%, preferably at least 50%, ideally at least 60%, of the area of main surfaces. In addition, the high-iodide epitaxial phases account for at least 10 mole %, preferably at least 15 mole %, of total amount of silver.
Furthermore, the suitable occupying areal proportion of the high-iodide epitaxial phases in each individual grain is within xc2x110%, preferably xc2x18%, of an average occupying areal proportion for all the grains. By such an areal proportion control, a further improvement in image sharpness can be made.
Since the present epitaxial phases contain silver iodide in high proportions, the solubility thereof is lowered and the shape thereof is kept stable, and further the iodide ions present on the surface of epitaxy can enhance adsorption of sensitizing dyes.
A main reason why many high-iodide epitaxial phases are formed on the main surfaces of host tabular grains as in the present invention is thought to be a difference in lattice parameter between the host grain component and the high-iodide epitaxial phase component. The lattice parameters of silver halide compositions are described, e.g., in T. H. James The Theory of the Photographic Process, 4 th ed., pp. 3-4, Macmillan Publishing Co., Inc. (1977). Since a great difference in lattice parameter between a host tabular grain and a high-iodide epitaxial phase has an effect on epitaxial growth in the plane direction of the host tablet, epitaxial growth in the other directions takes place after the growth in the plane direction proceeds until the time when the relief of structural distortion becomes impossible or in parallel with the growth in the plane direction. Therefore, it is thought that many high-iodide epitaxial phases are formed on the main surfaces of host tabular grains. Further, the smaller the difference in lattice parameter between the main surface of a host tabular grain and a high-iodide epitaxial phase, namely the higher the silver iodide content in the main surface of a host tabular grain, the easier the formation of the high-iodide epitaxial phase. This is because the structural distortion can be reduced by narrowing the lattice parameter difference. In addition, the high-iodide epitaxial phases formed on a host portion having a high silver iodide content lose boundaries between neighboring epitaxial phases to result in formation of continuous high-iodide layer over the whole main surface.
In the present invention, it is appropriate that the formation of high-iodide epitaxial phases on the main surfaces of host tabular grains be performed at a silver potential in the range of +30 mV to +160 mV (reference electrode: saturated calomel electrode), preferably from +60 mV to +150 mV. In order to deposit the epitaxial phases specifically on a central part of the main surface, but not on the fringe part and lateral faces, of each individual host tabular grain, it is advantageous to choose a high silver potential. In this case, however, the epitaxial phases deposited lose boundaries between neighboring epitaxial phases and form a continuous high iodide layer. Further, the formation under a high temperature is preferred, and so the formation temperature is adjusted to the range of 50xc2x0 C. to 80xc2x0 C., preferably 55xc2x0 C. to 65xc2x0 C. Although the grain formation methods are shown specifically in Examples, potential-controlled double jet methods are used to advantage. The suitable addition speed at the time when high-iodide epitaxial phases are formed is from 0.1 g/min to 0.7 g/min, preferably from 0.2 g/min to 0.6 g/min, based on AgNO3. Although the adjustment to a high potential is effective for increasing the number of high-iodide epitaxial phases formed on the main surface, it causes a loss of boundaries between neighboring epitaxial phases to result in formation of a continuous high iodide layer over the whole main surface.
The present silver halide grains are prepared using gelatin as a protective colloid. As the gelatin, alkali-processed gelatin is in common use. It is favorable in particular to use alkali-processed gelatin having undergone deionization treatment for removal of foreign ions and impurities and ultrafiltration treatment. As examples of usable gelatin besides alkali-processed gelatin, mention may be made of acid-processed gelatin, gelatin of low molecular weight (in the range of 1,000 to 8xc3x97104, such as enzymatically decomposed gelatin, acid- and/or alkali-hydrolyzed gelatin or thermally decomposed gelatin), gelatin of high molecular weight (in the range of 1.1xc3x97105 to 3.0xc3x97105), gelatin with a methionine content of 50 xcexcmol/g or below, gelatin with a tyrosine content of 20 xcexcmol/g or below, acid-processed gelatin containing methionine groups reduced in number, gelatin containing methionine groups deactivated by alkylation, and variously modified gelatin as recited below. The gelatin of high molecular weight is disclosed in Japanese Patent Application (Laid-Open) No. 237704/1999, 233962/2001 and 281780/2001. Examples of variously modified gelatin include gelatin whose amino groups are modified, such as phthalated gelatin, succinated gelatin, trimellitated gelatin or pyromellitated gelatin, and gelatin whose carboxylic groups are modified, such as esterified gelatin represented by methyl esterified gelatin, amidated gelatin, and imidazole-modified gelatin such as ethoxyformylated gelatin. These gelatin derivatives may be used alone or as mixtures of two or more thereof. The amount of gelatin used in the step of forming the present grains is from 1 g to 60 g per mole silver, preferably from 3 g to 40 g per mole silver. The suitable gelatin concentration in the step of chemical sensitization in the present invention is from 1 to 100 g/mole silver, preferably 1 to 70 g/mole silver.
In forming the present host tabular grains, grain growth of at least 10% of the host tabular grains, based on silver, though may be conducted adding fine grains of silver iodobromide prepared in advance to a vessel in which the grain growth is carried out, is preferably performed in a vessel while adding thereto fine grains of silver iodobromide continuously formed in a vessel other than the vessel for the grain growth. The size of fine grains of silver iodobromide added is from 0.005 to 0.05 xcexcm, preferably from 0.01 to 0.03 xcexcm. The suitable temperature at the time of grain growth is from 60xc2x0 C. to 90xc2x0 C., preferably from 70xc2x0 C. to 85xc2x0 C.
Improvements in photographic properties matching the described advantages can be realized by chemically sensitizing the host tabular grains, although this chemical sensitization is not essential to carrying out the present invention. It has also proved possible to introduce chemical sensitizers to the host tabular grains together with high iodide epitaxial phases while completely avoiding an increase in the thickness of host tabular grains.
For achieving further improvements in photographic properties by chemical sensitization, it has proved effective to form a second epitaxially crystallized part restrictively on the corners of host tabular grains in addition to joining high-iodide epitaxial phases to the host tabular grains. The suitable amount of silver in the epitaxial part joined to the corners is from 2 to 30%, preferably from 5 to 15%, of the total amount of silver. The suitable chemical composition in the corner epitaxial part may be any of silver chloride, silver chlorobromide, silver chlorobromoiodide, silver iodobromide and silver thiocyanate. Of these compositions, silver chloride, silver chlorobromide and silver chlorobromoiodide are preferred.
In the present invention, it is specifically planned that one or more dopants is incorporated in the crystal lattice structure of either the host tabular grains or the second epitaxial phases limited to the corners. When two or more dopants are incorporated, it is specifically planed to place one dopant in the host tabular grains and another in the second epitaxial phases, thereby avoiding antagonistic effects capable of occurring when dissimilar dopants are present in the same grain region. Any of dopants known to be useful in FCCRS crystal lattice can be incorporated. Photographically useful dopants selected from a wide range of periods and groups in the Periodic Table of Elements have been reported. Examples of conventionally used dopants include ions from the periods 3 to 7 (most commonly the periods 4 to 6) in the Periodic Table of Elements, such as Fe, Co, Ni, Ru, Rh, Pd, Re, Os, Ir, Pt, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Mo, Zr, Nb, Cd, In, Sn, Sb, Ba, La, W, Au, Hg, Tl, Pb, Bi, Ce and U. By using dopants, (a) the sensitivity can be increased, (b) high or low intensity reciprocity failure can be reduced, (c) variation of contrast can be increased, decreased or reduced, (d) pressure sensitivity can be lowered, (e) dye desensitization can be decreased, (f) stability can be enhanced (wherein reduction in thermal instability is included), (g) minimum density can be lowered and/or (h) maximum density can be heightened. In some uses, polyvalent metal ions are effective. These metals can be added in the form of salts capable of being dissolved at the time of grain formation, such as ammonium salt, acetate, nitrate, sulfate, phosphate, hydroxide, six-coordinated complex salt and four-coordinated complex salt As examples of such salts, mention may be made of CdBr2, CdCl2, Cd(NO3)2, Pb(NO3)2, Pb(CH3COO)2, K3[Fe(CN)6], (NH4)4[Fe(CN)6], K3IrCl6, (NH4)3RhCl6 and K4[Ru(CN)6]. Ligands of coordination compounds can be selected from halo, aquo, cyano, cyanato, thiocyanato, nitrosil, thionitrosil, oxo and carbonato ligands. These metal compounds may be used alone or as a combination of two or more thereof.
It is preferable that the metal compounds be dissolved in water or an appropriate organic solvent, such as methanol or acetone, and then added. In order to stabilize the solution, a method of adding a water solution of hydrogen halide (e.g., HCl, HBr) or alkali halide (e.g., KCl, NaCl, KBr, NaBr) can be used. Further, if desired, an acid or an alkali maybe added. The metal compounds can be added to a reaction vessel before or during the grain formation. In the other way, the metal compounds may be added continuously during the formation of silver halide grains by adding them to aqueous solutions of water-soluble salt (e.g., AgNO3) or alkali halide (e.g., NaCl, KBr, KI). In addition, a solution of metal salt is prepared independently of the solution of water-soluble salt and the solution of alkali halide, and added continuously in an appropriate stage during the grain formation. And it is also preferred to use various combinations of addition methods.
The chemical sensitization in the present invention can be effected using chalcogen sensitization including sulfur sensitization, selenium sensitization and tellurium sensitization, precious metal sensitization (especially gold sensitization) and reduction sensitization individually or as combinations thereof. In particular, reduction sensitization is effective for the present emulsion.
In the sulfur sensitization, unstable sulfur compounds are used. Such unstable sulfur compounds are described, e.g., in P. Glafkides, Chimie et Physique Photographique, 5th ed., Paul Montel (1987), and Research Disclosure vol. 307, Item 307105. Specifically, known sulfur compounds, such as thiosulfates (e.g., sodium thiosulfate), thioureas (e.g., diphenylthiourea, triethylthiourea, N-ethyl-Nxe2x80x2-(4-methyl-2-thiazolyl) thiourea, dicarboxymethyl-dimethylthiourea and carboxymethyl-trimethylthiourea), thioamides (e.g., thioacetamide), rhodanines (e.g., diethylrhodanine and 5-benzylidene-N-ethyl-rhodanine), phosphine sulfides (e.g., trimethylphosphine sulfide), thiohydantoins, 4-oxo-oxazolidine-2-thiones, dipolysulfides (e.g., dimorpholine disulfide, cystine and hexathiokane-thione), mercapto compounds (e.g., cysteine), polythionates and elemental sulfur, can be used for sulfur sensitization. In addition, active gelatin is also utilizable. Of the compounds recited above, thiosulfates, thioureas, phosphine sulfides and rhodanines are preferred over the others.
In the selenium sensitization, unstable selenium compounds are used. The unstable selenium compounds which can be used herein are disclosed in Japanese Patent Application (Laid-Open) Nos. 13489/1968, 15748/1969, 25832/1992 and 109240/1992, 271341/1992 and Japanese Patent Application No. 82929/1991. Specifically, such compounds include colloidal metallic selenium, selenoureas (such as N,N-dimethylselenourea, trifluoro-methylcarbonyltrimethylselenourea and acecyl-trimethylselenourea), selenoamides (such as selenoacetamide and N,N-diethylphenylselenoamide), phosphine selenides (such as triphenylphosphine selenide and pentafluorophenyl-triphenylphosphine selenide), selenophosphates (such as tri-p-tolylselenophosphate and tri-n-butylselenophosphate), selenoketones (such as selenobenzophenone), isoselenocyanates, selenocarboxylic acids, selenoesters and diacylselenides. In addition, moderately stable selenium compounds (as disclosed in Japanese Patent Publication Nos. 4553/1971 and 34492/1977), including selenious acid, potassium selenocyanide, selenazoles and selenides, can also be utilized for selenium sensitization.
In the tellurium sensitization, unstable tellurium compounds as disclosed in Canadian Patent No. 800,958, U.K. Patent Nos. 1,295,462 and 1,396,696, and Japanese Patent Application (Laid-Open) Nos. 204640/1992, 271341/1992, 333043/1992 and 303157/1993 can be used. Examples of such tellurium compounds include telluroureas (such as tetramethyltellurourea, N,Nxe2x80x2-dimethylethylenetellurourea and N,Nxe2x80x2-diphenylethylene-tellurourea), phosphine tellurides (such as butyldiisopropylphosphine telluride, tributylphosphine telluride, tributoxyphosphine telluride and ethoxydiphenylphosphine telluride), diacyl(di)tellurides (such as bis(diphenylcarbamoyl)ditelluride, bis(N-phenyl-N-methylcarbamoyl)ditelluride, bis (N-phenyl-N-methyl-carbamoyl) telluride and bis(ethoxycarbonyl)telluride), isotellurocyanates, telluroamides, tellurohydrazides, telluroesters (such as butylhexyltelluroester), telluroketones (such as telluroacetophenone), colloidal tellurium, (di) tellurides and other tellurium compounds (such as potassium telluride and sodium telluropentathionate). Of these tellurium compounds, diacyl(di)tellurides and phosphine tellurides are preferred over the others.
In the gold sensitization can be used gold salts as described in, e.g., P. Glafkides, Chimie et Physique Photographique, 5th ed., Paul Montel (1987), and Research Disclosure, vol. 307, Item 307105. Examples of such gold salts include chloroauric acid, potassium chloroaurate and potassium aurithiocyanate. In addition to these gold salts, the gold compounds disclosed in U.S. Pat. No. 2,642,361 (gold sulfide and gold selenide), U.S. Pat. No. 3,503,749 (gold thiolate having water-soluble groups), U.S. Pat. No. 5,049,484 (bis(methylhydantoinato) gold complex salt), U.S. Pat. No. 5,049,485 (mesoionic thiolate-gold complex salts, such as 1,4,5-trimethyl-1,2,4-triazolium-3-thiolate-gold complex salt), the large hetero ring-gold complex salts disclosed in U.S. Pat. Nos. 5,252,455 and 5,391,727, and the gold compounds disclosed in U.S. Pat. Nos. 5,620,841, 5,700,631, 5,759,760, 5,759,761, 5,912,111, 5,912,112 and 5,939,245, and Japanese Patent Application (Laid-Open) Nos. 147537/1989, 69074/1996, 69075/1996, 269554/1997 and 29274/1970, German Patent Nos. DD-264524A, 264525A, 264574A and 298321A, Japanese Patent Application (Laid-Open) Nos. 75214/2001, 75215/2001, 75216/2001, 74217/2001 and, 75218/2001 can be used for the gold sensitization.
In the reduction sensitization can be used known reducing compounds as described in, e.g., P. Glafkides, Chimie et Physuque Photographique, 5th ed., Paul Montel (1987), and Research Disclosure, vol. 307, Item 307105. Examples of such reducing compounds include aminoiminomethanesulfinic acid (thiourea dioxide), borane compounds (such as dimethylamine borane), hydrazine compounds (such as hydrazine and p-tolylhydrazine), polyamine compounds (such as diethylene-triamine and triethylenetetramine), stannous chloride, silane compounds, reductones (such as ascorbic acid), sulfites, aldehyde compounds and hydrogen gas. In addition, reduction sensitization can be carried out in an atmosphere of high pH or excess silver ions (the so-called silver ripening).
The chemical sensitization of those kinds may be carried out independently or in combination of two or more thereof. In particular, the combination of chalcogen sensitization and gold sensitization is preferred over the others. Further, it is effective that the reduction sensitization be carried out in the step of forming silver halide grains. The amount of chalcogen sensitizers used in the present invention is determined depending on what type of silver halide grains are sensitized and what condition is adopted for the chemical sensitization. Specifically, the amount of chalcogen sensitizers used is generally from 10xe2x88x928 to 10xe2x88x922 mole, preferably from 10xe2x88x927 to 5xc3x9710xe2x88x923 mole, per mole of silver halide. The amount of precious metal sensitizers used is generally from 10xe2x88x927 to 10xe2x88x922 mole per mole of silver halide. As to the conditions for chemical sensitization, there are no particular restrictions in the present invention. However, it is appropriate for the chemical sensitization that the pAg be from 6 to 11, preferably from 7 to 10, the pH be from 4 to 10, and the temperature be from 40 to 95xc2x0 C., preferably 45 to 85xc2x0 C.
In order to prevent fogging from occurring in photosensitive materials during the production, storage or photographic processing process, or stabilize photographic properties, it is desirable to add various compounds to the silver halide emulsion. Examples of such compounds include azoles (such as benzothiazolium salts, nitroindazoles, triazoles, benzotriazoles, imidazoles and benzimidazoles (especially nitro- or halogen-substituted benzimidazoles)), heterocyclic mercapto compounds (such as mercaptothiazole, mercaptobenzothiazoles, mercaptobenzimidazoles, mercapto-thiadiazoles, mercaptotetrazoles (especially 1-phenyl-5-mercaptotetrazole) and mercpatopyrimidines), heterocyclic mercapto compounds having the same heterocyclic moieties as recited above and further containing water soluble groups, such as carboxyl and sulfo groups, thioketo compounds (such as oxazinethione), azaindenes (such as tetrazaindenes (especially 4-hydroxy-(1,3,3a,7)tetrazaindens), benzene-thiosulfonic acids and benzenesulfinic acids. In general these compounds are known as antifoggants or stabilizers.
The antifoggants or stabilizers are usually added after chemical sensitization. However, their addition timing can be chosen from the midst of chemical sensitization, or any of stages before chemical sensitization. More specifically, in the process of forming silver halide emulsion grains, the antifoggants or stabilizers may be added during the addition of a silver salt solution, in a period between the conclusion of the addition and the start of chemical sensitization, or in the course of chemical sensitization (preferably within a period between the start and 50%, particularly preferably 20%, of the time spent on chemical sensitization).
The present silver halide photographic materials have no particular restrictions as to their layer structures. When they are silver halide color photographic materials, however, they have a multi-layer structure for recording blue light, green light and red light separately. Further, each silver halide emulsion layer may be constituted of two layers, namely a high-speed layer and a low-speed layer. Examples of a practical layer structure are given below:
(1) BH/BL/GH/GL/RH/RL/S
(2) BH/BM/BL/GH/GM/GL/RH/RM/RL/S
(3) BH/BL/GH/RH/GL/RL/S
(4) BH/GH/RH/BL/GL/RL/S
(5) BH/BL/CL/GH/GL/RH/RL/S
(6) BH/BL/GH/GL/CL/RH/RL/S
Herein, B stands for a blue-sensitive layer, G for a green-sensitive layer, R for a red-sensitive layer, H for a highest speed layer, M for a medium speed layer, L for a low speed layer, S for a support, and CL for an interlayer effect-providing layer. Light-insensitive layers, such as a protective layer, a filter layer, an interlayer and an anti-halation layer, are omitted from the foregoing representation of layer structures. In addition, the arranging order of high speed and low speed layers having the same color sensitivity may be reversed. The layer structure (3) is described in U.S. Pat. No. 4,184,876. The layer structure (4) is described in Research Disclosure, vol. 225, Item 22534, and Japanese Patent Application (Laid-Open) Nos. 177551/1984 and 177552/1984. The layer structures (5) and (6) are described in Japanese Patent Application (Laid-Open) No.34541/1986. The layer structures (1), (2) and (4) are preferred over the others. Besides color photographic materials, the present silver halide photosensitive materials can be applied to X-ray photographic materials, sensitive materials for black and white photography, sensitive materials for photomechanical process and photographic printing paper.
With respect to the gelatin hardeners, for example, active halogen compounds (such as 2,4-dichloro-6-hydroxy-1,3,5-triazine and sodium salt thereof) and active vinyl compounds (such as 1,3-bisvinylsulfonyl-2-propanol, 1,2-bis(vinylsulfonylacetamido)ethane and vinyl polymers having vinylsulfonyl groups in their chains) are used to advantage because they can quickly harden hydrophilic colloids such as gelatin to provide stable photographic characteristics. In addition, N-carbamoylpyridinium salts (such as (1-morpholinocarbonyl-3-pyridinio)methanesulfonate) and haloamidinium salts (such as 1-(1-chloro-1-pyridino-methylene)pyrrolidinium 2-naphthalenesulfonate) are also excellent hardeners because of their high hardening speed.
For various additives usable in the present silver halide emulsion (e.g., binders, chemical sensitizers, spectral sensitizers, stabilizers, gelatin, hardeners, surfactants, antistatic agents, polymer latexes, matting agents, color couplers, ultraviolet absorbents, discoloration inhibitors, dyes), supports and processing methods for photographic materials (e.g., coating methods, exposure methods, development-processing methods), the descriptions in Research Disclosure, vol. 176, Item 17643 (abbreviated as xe2x80x9cRD-17643xe2x80x9d), vol. 187, Item 18716 (abbreviated as xe2x80x9cRD-18716xe2x80x9d) and vol. 225, Item 22534 (abbreviated as xe2x80x9cRD-22534xe2x80x9d) can be referred to. The locations where the additives are described in each of those references are listed below.
The color photographic materials can be processed using the general methods described in Research Disclosure, vol. 176, Item 17643 and ibid., vol. 187, Item 18716. Specifically, the color photographic light-sensitive materials are subjected to washing or stabilization processing usually after undergoing development processing and bleach-fix or fixation processing. In the washing step, a counter-current washing method using two or more tanks is generally adopted to effect a water saving. As a typical example of stabilization processing which can take the place of washing processing, the multistage counter-current stabilization processing as disclosed in Japanese Patent Application (Laid-Open) No. 8543/1982 can be cited.